What helps
A conversion that went wrong is much easier to fix with three things: which formats you were going between, which browser you were using, and what actually happened - a message on screen, a file that would not open, a tab that sat there.
There is no need to send the file. It would not help much, and the whole point of this site is that your files stay on your machine - that does not stop being true because something broke. Naming the format is enough.
Asking for a format
Requests are worth sending. The list has grown mostly by people wanting something that was not there. Worth knowing that some formats cannot be done honestly in a browser - anything needing a patent-licensed decoder the browser does not already have - so a request may come back as an explanation rather than a conversion.
Privacy
Writing in is the only way this site ever learns anything about anyone, and only because you chose to. There is no form here, no account and no tracking: see the privacy policy for what that means in detail.